I like to think of it like this. A Router alert is a messaging saying "Hey Routers. You MIGHT be interested in the body(payload. Other ext headers) of this packet"
A HBH is a message saying "Hey ALL NODES in transit. You MUST look in the HBH and do what it says" Hope that helps... (hi john) -Brian http://consult.tavian.com/ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Spence Sent: Tuesday, November 01, 2005 7:31 PM To: 'Fred Baker' Cc: ipv6@ietf.org Subject: RE: Question about the need for a "Router Alert Option" (RFC 2711)within a Hop-By-Hop Option Extension Header (RFC 2460) ... Sorry - that fired too fast. RFC 2711 also references RFC 2460, so it was built for the H-B-H extension header. Also, if you look at RFC 3810 (MLDv2), it also references the Router Alert Option and says: All MLDv2 messages described in this document MUST be sent with a link-local IPv6 Source Address, an IPv6 Hop Limit of 1, and an IPv6 Router Alert option [RFC2711] in a Hop-by-Hop Options header. (The Router Alert option is necessary to cause routers to examine MLDv2 messages sent to IPv6 multicast addresses in which the routers themselves have no interest.) So, I still don't understand the Router Alert Option, but I see a number of places where it is referenced. [[Spence]] ________________________________ From: John Spence [mailto:[EMAIL PROTECTED] Sent: Tuesday, November 01, 2005 7:25 PM To: 'Fred Baker' Cc: 'ipv6@ietf.org' Subject: RE: Question about the need for a "Router Alert Option" (RFC 2711) within a Hop-By-Hop Option Extension Header (RFC 2460) ... Thanks for the quick reply. The Router Alert Option (RFC 2711) is dated October 1999. It says "This memo describes a new IPv6 Hop-by-Hop Option type ", so the Router Alert is designed for the H-B-H Extension header. ---------------------------------------------------- John Spence, CCSI, CCNA, CISSP Native6, Inc. IPv6 Training and Consulting [EMAIL PROTECTED] (wk) 206-682-0275 www.native6.com ---------------------------------------------------- ________________________________ From: Fred Baker [mailto:[EMAIL PROTECTED] Sent: Tuesday, November 01, 2005 6:48 PM To: John Spence Cc: ipv6@ietf.org Subject: Re: Question about the need for a "Router Alert Option" (RFC 2711) within a Hop-By-Hop Option Extension Header (RFC 2460) ... one of them sounds like it is redundant. I think the Router Alert predated the HBH header... On Nov 1, 2005, at 6:04 PM, John Spence wrote: Hello; If the H-B-H extension header means "all intermediate nodes must look in here for options to process", why is the "Router Alert" option needed? As I read the text of the two RFCs, the Router Alert Option is redundant - just including a H-B-H header means "intermediate nodes must look at this packet even if it is not addressed to them", which seems to be the same meaning as Router Alert. I must be missing something. Can someone provide a quick answer, or a pointer to the answer so I can research it myself? Thanks very much. John Spence ----------------------------------------------------------------- --- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6 ----------------------------------------------------------------- --- -------------------------------------------------------------- "Don't worry about the world coming to an end today. It's already tomorrow in Australia." (Charles Schulz ) -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6 -------------------------------------------------------------------- -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
